Hydrothermal synthesis of a two-dimensional g-C₃N₄/MoS₂/MnOOH composite material and its potential application as photocatalyst

BACKGROUND: Environmental pollution and energy crisis are nowadays considered among the most important problems facing humanity. Several strategies have been proposed to solve them, being photocatalysis a very promising one because of its ease of application and low cost. In the search for active photocatalysts, those based on graphite-like carbon nitride (g-C₃N₄) are becoming good alternatives for various reactions. In this work, the properties of g-C₃N₄/MoS₂/MnOOH composite material and its photocatalytic behavior for the production of hydrogen (H₂) under UV radiation were investigated. RESULTS: The composite material was synthesized by applying a combination of thermal condensation and hydrothermal methods. According to the results of X-ray diffraction (XRD), ultraviolet diffuse reflectance spectroscopy (UV-DRS), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM), good dispersion of the phases and the formation of a heterojunction were observed. The band gap value of the composite material, calculated by the Kubelka–Munk equation using the values obtained from UV-DRS analysis, was lower than those of the individual components, while it also had a much longer electron–hole recombination time, according to photoluminescence analysis. As a consequence of a synergistic effect, the activity of the proposed composite photocatalyst was superior in the reaction of water splitting, with a kinetic constant of 466 μmol h⁻¹ and a production rate of 1750 μmol H₂ g⁻¹ _cat h⁻¹ (50 and 21% higher than those obtained with MoS₂ and g-C₃N₄, respectively). CONCLUSION: Because of its high activity and stability, g-C₃N₄/MoS₂/MnOOH composite photocatalyst is an excellent alternative for H₂ production by the water splitting reaction.